In particular, milling tools are used on so-called ground milling machines, more particularly, road milling machines, recyclers, and stabilizers which have suitable milling tool holders distributed over the external cylindrical surface of a supporting barrel and held in place thereon. This overall unit is usually referred to as the “milling drum” and in such ground milling machines is usually driven on the chassis and is mounted for rotation about a horizontal axis extending transversely to the direction of travel and under working conditions cuts into the ground. The ground material is milled to the desired milling depth. Typically, the milling tools are designed, for example, as round shank chisels in known manner. The milling tools are each held by a milling tool holder that forms the link between the milling tool and the supporting barrel. Such generic milling tool holders comprise a base plate having a bottom surface for attachment to the supporting barrel of the milling drum and a top surface opposite to the bottom surface. The base plate is, thus, that part which in the installed state faces the supporting barrel and, in particular, is connected directly to the cylindrical exterior surface of the supporting barrel, for example, by a welded and/or bolted joint. The bottom surface of the base plate, as regarded in the radial direction of the supporting barrel, is opposite to the upper surface of the base plate, which, thus, describes that surface of the base plate that forms the outer surface of the base plate in the installed state. Furthermore, there is present a holding element that protrudes from the upper surface of the base plate and serves to accommodate the milling tool. For this purpose, there is present in the holding member a receiving channel for the milling tool, which channel extends from its forward side to its rearward side, as regarded in the direction of rotation of the milling tool. More specifically, the receiving channel accommodates, for example, the shank of a round shank chisel. “Direction of rotation” in this context refers to the direction of movement of the milling drum, or the milling tool holder in its installed state on the supporting barrel, in the operational mode. The direction of rotation is naturally oriented toward the working tip of the milling tool. The receiving channel is an ideally linear through bore in the holding member, which can be additionally equipped, for example, with rinsing ports and/or other features.
In order to facilitate smooth working operation of the rotating milling drum, usually a plurality of milling tools or milling tool holders are disposed on the supporting barrel. The unit, or tool assembly, consisting of at least two milling tool holders disposed in the peripheral direction one behind the other is hereinafter referred to as a “composite tool” or “composite tool holder” respectively. Alternatively, the “composite tool” could be designated as “tool group” or “tool unit” that includes at least two milling tools and milling tool holders, respectively. The milling tool holders are disposed in the peripheral direction one behind the other and with an offset in the axial direction of the axis of rotation of the milling drum, in order to make milling possible over the entire axial length, i.e., the width, of the milling drum. To this end, the milling tools are frequently disposed on the peripheral surface of the supporting barrel in the form of helices, which extend, depending on the embodiment, for example, in each case toward the center to cause the milled material to be transported in this direction so as to facilitate the removal of the milled material, for example, from a milling drum box. Appropriate arrangements are also known in the prior art. The present invention thus, more particularly, also relates to a composite tool for a milling drum having at least one forward milling tool holder, as regarded in the direction of rotation of the milling drum and at least one rearward milling tool holder, as regarded in the peripheral direction of the milling drum, disposed directly behind said forward milling tool holder with an offset therefrom in the axial direction of the axis of rotation of the milling drum, each of the milling tool holders being adapted to accommodate a milling tool, more particularly, a round shank chisel. At least two of the milling tool holders of the composite tool according to the present invention are thus disposed, as regarded in the peripheral direction of the milling drum, in direct succession and, more particularly, flush with one another and, very particularly, positively connected, at least partially, to each other, such that the ground milling action of the at least two milling tools is carried out first by the milling tool in the forward milling tool holder and then, slightly offset in the axial direction of the axis of rotation, by the milling tool in the rearward milling tool holder.
The number and density of the milling tools disposed on the supporting barrel bearing the milling tools, that is to say, the milling tool holders, can vary greatly depending on the application. In particular, in the case of so-called micro fine milling, which is not primarily concerned with a deep and large-volume extraction of material, but rather with increasing or restoring the skid resistance and/or flatness of a road surface, there is frequently a particularly dense arrangement of milling tools on the supporting barrel of the milling drum. In micro fine milling, often only a few millimeters of the top layer are removed, in particular, for the repair of roads, where a surface roughness of only a few millimeters is tolerated. The individual milling tools are thus disposed in line spaced at intervals of usually up to 6 millimeters on the supporting barrel. The linear distance between two milling tools corresponds to the distance of the cutting circles of the two tools, as regarded in the axial direction of the axis of rotation of the milling drum. This does not necessarily have to apply to two milling tools disposed directly one behind the other, as regarded in the direction of rotation.
When in operation, milling tools are naturally exposed to considerable wear effects, so that frequent replacement of the milling tools is required. Especially, in the case of milling drums used for micro fine milling, is this procedure, however, extremely complicated, particularly because of the dense arrangement of the milling tools. The space available is very narrow and complicates the exchange of individual milling tools, especially when the chisel has to be removed from the rear of the receiving channel toward the front, for example, by means of a chisel extractor. Accordingly, in such situations involving conventional milling drums, crushing of the operator's hands or other injuries will often occur. Or access to the rear is blocked and the round shank chisels must be pulled out or knocked out via the chisel head.
The object of the present invention is to provide a composite tool, a milling tool holder and a milling drum that are particularly suitable for micro fine milling involving narrow linear spacing of the milling cutters, making possible improved replacement of the milling tools over the prior art.